1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and particularly to a control system in which an engine operating parameter (torque related parameter) related to the engine output torque is calculated according to the exhaust gas recirculation ratio, and the engine is controlled using the calculated torque related parameter.
2. Description of the Related Art
In the control system for an internal combustion engine, the torque demand control (torque base control) is used in recent years, as shown in Japanese patent laid-open No. 2006-29194 (JP-'194). In the torque demand control, a target torque of the engine is calculated according to a vehicle control demand torque which is necessary for the transmission control or the traction control, as well as the driver's demand torque. Further, an actual output torque of the engine is estimated or detected, and the intake air amount (fuel supply amount) and/or the ignition timing of the engine are controlled so that the actual output torque coincides with the target torque.
Japanese patent laid-open No. 2003-269306 (JP-'306) discloses a control system for an internal combustion engine, wherein a residual gas ratio (an internal exhaust gas recirculation ratio), which is a residual ratio of burned gases remaining in the combustion chamber after combustion, is calculated, and the ignition timing is controlled according to the residual gas ratio. According to this control system, the residual gas ratio is calculated based on the engine rotational speed, the valve overlap amount (an overlapped period of the valve opening periods corresponding to the intake valve and the exhaust valve), the intake pressure, the exhaust gas temperature, and the intake air amount.
Further, a known control system for an internal combustion engine having an exhaust gas recirculation mechanism, uses a method for calculating an exhaust gas recirculation ratio using a map for calculating the exhaust gas recirculation ratio (the external exhaust gas recirculation ratio) set according to an opening of the exhaust gas recirculation control valve.
In the torque base control, it is necessary to estimate the actual output torque based on the engine operating parameter. In the system shown in JP-′ 194, the actual output torque is calculated by retrieving tables or maps according to the intake air amount, the engine rotational speed, the air-fuel ratio, the ignition timing, and a parameter indicative of the intake valve operating condition. Accordingly, the man power necessary for setting the tables or maps is comparatively large.
Regarding the calculation method of the residual gas ratio shown in JP-′306, the number of parameters applied to the calculation is comparatively large. Accordingly, there is a similar problem that the man power necessary for setting the tables or maps becomes large. Further, in the conventional method for calculating the external exhaust gas recirculation ratio, many maps are necessary corresponding to various operating conditions.
Therefore, more tables or maps are necessary for performing the torque demand control taking the exhaust gas recirculation ratio into account, wherein the exhaust gas recirculation ratio is calculated according to both of the internal exhaust gas recirculation amount and the external exhaust gas recirculation amount, which requires much more man power for setting tables or maps.